The present invention relates to a magnetic head, and a head suspension assembly and a magnetic disk apparatus which use the magnetic head.
With the trend to a larger capacity and a smaller size of hard disk drives (HDD), heads are required to have a higher sensitivity and a larger output. To meet these requirements, strenuous efforts have been made to improve the characteristics of GMR heads (Giant Magneto-Resistive Head) currently available on the market. On the other hand, intense development is under way for a tunnel magneto-resistive head (TMR head) which can be expected to have a resistance changing ratio twice or more higher than the GMR head.
Generally, the GMR head differs from the TMR head in the head structure due to a difference in a direction in which a sense current is fed. A head structure adapted to feed a sense current in parallel with a film surface, as in a general GMR head, is referred to as a CIP (Current In Plane) structure, while a head structure adapted to feed a sense current perpendicularly to a film surface, as in the TMR head, is referred to as a CPP (Current Perpendicular to Plane) structure. Since the CPP structure can use a magnetic shield itself as an electrode, it is essentially free from short-circuiting between the magnetic shield and a device (defective insulation) which is a serious problem in reducing a lead gap in the CIP structure. For this reason, the CPP structure is significantly advantageous in providing a higher recording density.
Other than the TMR head, also known as a head in CPP structure is, for example, a CPP-GMR head which has the CPP structure, though a spin valve film (including a specular type and dual spin valve type magnetic multilayer film) is used for a magneto-resistive device.
Irrespective of the CIP structure or CPP structure, in a magnetic head using a magneto-resistive device, a lower magnetic shield layer and an upper magnetic shield layer are disposed on and blow a magneto-resistive layer in order that the magneto-resistive device limitatively senses only magnetic flux from an opposite location of a magnetic recording medium and shield other magnetic flux. Then, in order to increase the resolution of the magneto-resistive device with the intention to increase the recording density, a shield gap reduction strategy has been under way to narrow down the gap between the lower magnetic shield layer and upper magnetic shield layer.
In a CIP-based magnetic head, a lower magnetic shield layer and an upper magnetic shield layer are electrically insulated from a magneto-resistive layer and a first and a second lead layer which apply a sense current to the magneto-resistive layer in parallel with the film plane in the magneto-resistive layer. In a CPP-based magnetic head, in turn, a lower magnetic shield layer and an upper magnetic shield layer are connected to a first and a second lead layer, respectively, such that the first and second lead layers apply a sense current to a magneto-resistive layer through a lower magnetic shield layer and an upper magnetic shield layer perpendicularly to the film plane in the magneto-resistive layer. In the conventional CPP-based magnetic head, the lower magnetic shield layer and first lead layer are integrally and continuously made of the same magnetic material, and the upper magnetic shield layer and second lead layer are integrally and continuously made of the same magnetic material.
For designing and manufacturing such a magnetic head, it is critical to measure its magnetic characteristics for evaluation. Generally, the evaluation of the magnetic characteristics for magnetic heads involves measuring dynamic characteristics for evaluation or measuring static characteristics for evaluation.
The evaluation of dynamic characteristics involves mounting a magnetic head slider on a suspension to actually float the magnetic head slider above a magnetic recording medium, and measuring the characteristics of the magnetic head in a situation close to an actual use environment in a magnetic disk apparatus for evaluation. On the other hand, the evaluation of static characteristics involves externally applying a magnetic head with a uniform magnetic field generated by a magnetic field generating means instead of a magnetic field from a magnetic recording medium, and measuring the characteristics of the magnetic head under the applied magnetic field for evaluation.
The static characteristic evaluation method can be readily practiced as compared with the dynamic characteristic evaluation method because of its ability to evaluate the characteristics under a different environment from an actual use environment of a magnetic disk apparatus, the ability to evaluate the characteristics without mounting a magnetic head on a suspension and without floating the magnetic head above a magnetic recording medium, and the like. Moreover, in a manufacturing process, the static characteristic evaluation method can evaluate magnetic heads at an earlier stage before the magnetic heads are independently completed. Thus, from a viewpoint of efficient sorting of products, rapid feedback to magnetic head designing, and the like, the static characteristic evaluation is used as a very convenient and effective method for evaluating the characteristics of reproducing head devices.
An important point in the static characteristic evaluation is a high correlation exhibited thereby between the static characteristic evaluation and the dynamic characteristic evaluation which is performed under an actual use environment of a magnetic disk apparatus. If the correlation is low, a part (for example, a wafer or a bar (bar-shaped magnetic head aggregate) cut from a wafer) which can form part of a magnetic head that has good dynamic characteristics is likely to be determined as defective by the static characteristic evaluation, and is therefore discarded, or on the contrary, a part which can only form part of a magnetic head that has defective dynamic characteristics is likely to be determined as good by the static characteristic evaluation and used to complete a magnetic head.
However, it is known that the shield gap reduction strategy causes a problem of a lower correlation between the dynamic characteristics and static characteristics.
JP-A-2003-242613 discloses that a correlation between dynamic characteristics and static characteristics can be increased in a magnetic head by designing the magnetic head such that a lower magnetic shield layer and a higher magnetic shield layer have their shapes and sizes which substantially exactly overlap each other when viewed in a laminating direction (for example, Type 7 in Table 1 of JP-A-2003-242613). Also, JP-A-2003-242611 discloses a magnetic head which includes a lower magnetic shield layer and an upper magnetic shield layer that have their shapes and sizes which substantially exactly overlap each other when viewed in a laminating direction (for example, Type 4 in Table 1 of JP-A-2003-242611).
The present inventors have confirmed through the experiment described later that in a CPP-based magnetic head, the correlation between the dynamic characteristics and static characteristics becomes higher in comparison with a magnetic head which has one magnetic shield layer larger than the other magnetic shield layer, when a lower magnetic shield layer and a higher magnetic shield layer have their shapes and sizes which substantially exactly overlap each other when viewed in a laminating direction in accordance with the teaching in the aforementioned JP-A-2003-242613. In this event, like the conventional CPP-based magnetic head described above, the lower magnetic shield layer and first lead layer were integrally and continuously made of the same magnetic material, and the upper magnetic shield layer and second lead layer were integrally and continuously made of the same magnetic material.
While the correlation between the dynamic characteristics and static characteristics can be made higher by applying the technique taught by the aforementioned JP-A-2003-242613 to the conventional CPP-based magnetic head in the foregoing manner, it should be understood that an ever higher correlation between the dynamic characteristics and static characteristics is desired.